Index: include/__config =================================================================== --- include/__config +++ include/__config @@ -454,6 +454,10 @@ #define _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK __attribute__((__no_sanitize__("unsigned-integer-overflow"))) #endif +#if __has_builtin(__builtin_launder) +#define _LIBCPP_COMPILER_HAS_BUILTIN_LAUNDER +#endif + #elif defined(_LIBCPP_COMPILER_GCC) #define _ALIGNAS(x) __attribute__((__aligned__(x))) @@ -536,6 +540,10 @@ #define _LIBCPP_HAS_NO_ASAN #endif +#if _GNUC_VER >= 700 +#define _LIBCPP_COMPILER_HAS_BUILTIN_LAUNDER +#endif + #elif defined(_LIBCPP_COMPILER_MSVC) #define _LIBCPP_TOSTRING2(x) #x Index: include/new =================================================================== --- include/new +++ include/new @@ -46,6 +46,8 @@ new_handler set_new_handler(new_handler new_p) noexcept; new_handler get_new_handler() noexcept; +// 21.6.4, pointer optimization barrier +template constexpr T* launder(T* p) noexcept; // C++17 } // std void* operator new(std::size_t size); // replaceable @@ -250,6 +252,29 @@ } #endif +template +_LIBCPP_NODISCARD_AFTER_CXX17 inline +_LIBCPP_CONSTEXPR _Tp* __launder(_Tp* __p) _NOEXCEPT +{ + static_assert (!(is_function<_Tp>::value), "can't launder functions" ); + static_assert (!(is_same::type>::value), "can't launder cv-void" ); +#ifdef _LIBCPP_COMPILER_HAS_BUILTIN_LAUNDER + return __builtin_launder(__p); +#else + return __p; +#endif +} + + +#if _LIBCPP_STD_VER > 14 +template +_LIBCPP_NODISCARD_AFTER_CXX17 inline _LIBCPP_INLINE_VISIBILITY +constexpr _Tp* launder(_Tp* __p) noexcept +{ + return __launder(__p); +} +#endif + _LIBCPP_END_NAMESPACE_STD #endif // _LIBCPP_NEW Index: test/std/language.support/support.dynamic/ptr.launder/launder.nodiscard.fail.cpp =================================================================== --- test/std/language.support/support.dynamic/ptr.launder/launder.nodiscard.fail.cpp +++ test/std/language.support/support.dynamic/ptr.launder/launder.nodiscard.fail.cpp @@ -0,0 +1,27 @@ +// -*- C++ -*- +//===----------------------------------------------------------------------===// +// +// The LLVM Compiler Infrastructure +// +// This file is dual licensed under the MIT and the University of Illinois Open +// Source Licenses. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// + +// + +// template constexpr T* launder(T* p) noexcept; + +// UNSUPPORTED: c++98, c++03, c++11, c++14, c++17 +// UNSUPPORTED: clang-3.3, clang-3.4, clang-3.5, clang-3.6, clang-3.7, clang-3.8 + +#include +#include + +#include "test_macros.h" + +int main () +{ + int *p = nullptr; + std::launder(p); // expected-error {{ignoring return value of function declared with 'nodiscard' attribute}} +} Index: test/std/language.support/support.dynamic/ptr.launder/launder.pass.cpp =================================================================== --- test/std/language.support/support.dynamic/ptr.launder/launder.pass.cpp +++ test/std/language.support/support.dynamic/ptr.launder/launder.pass.cpp @@ -0,0 +1,35 @@ +//===----------------------------------------------------------------------===// +// +// The LLVM Compiler Infrastructure +// +// This file is dual licensed under the MIT and the University of Illinois Open +// Source Licenses. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// + +// + +// template constexpr T* launder(T* p) noexcept; + +// UNSUPPORTED: c++98, c++03, c++11, c++14 + +#include +#include + +#include "test_macros.h" + +constexpr int gi = 5; +constexpr float gf = 8.f; + +int main() { + static_assert(std::launder(&gi) == &gi, "" ); + static_assert(std::launder(&gf) == &gf, "" ); + + const int *i = &gi; + const float *f = &gf; + static_assert(std::is_same::value, ""); + static_assert(std::is_same::value, ""); + + assert(std::launder(i) == i); + assert(std::launder(f) == f); +} Index: test/std/language.support/support.dynamic/ptr.launder/launder.types.fail.cpp =================================================================== --- test/std/language.support/support.dynamic/ptr.launder/launder.types.fail.cpp +++ test/std/language.support/support.dynamic/ptr.launder/launder.types.fail.cpp @@ -0,0 +1,34 @@ +// -*- C++ -*- +//===----------------------------------------------------------------------===// +// +// The LLVM Compiler Infrastructure +// +// This file is dual licensed under the MIT and the University of Illinois Open +// Source Licenses. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// + +// + +// template constexpr T* launder(T* p) noexcept; +// The program is ill-formed if T is a function type or cv void. + +// UNSUPPORTED: c++98, c++03, c++11, c++14 + +#include +#include + +#include "test_macros.h" + +void foo() {} + +int main () +{ + void *p = nullptr; + (void) std::launder(( void *) nullptr); // expected-error-re@new:* {{static_assert failed{{.*}} "can't launder cv-void"}} + (void) std::launder((const void *) nullptr); // expected-error-re@new:* {{static_assert failed{{.*}} "can't launder cv-void"}} + (void) std::launder(( volatile void *) nullptr); // expected-error-re@new:* {{static_assert failed{{.*}} "can't launder cv-void"}} + (void) std::launder((const volatile void *) nullptr); // expected-error-re@new:* {{static_assert failed{{.*}} "can't launder cv-void"}} + + (void) std::launder(foo); // expected-error-re@new:* 1 {{static_assert failed{{.*}} "can't launder functions"}} +} Index: www/cxx1z_status.html =================================================================== --- www/cxx1z_status.html +++ www/cxx1z_status.html @@ -104,6 +104,7 @@ p0083r3LWGSplicing Maps and SetsOulu p0084r2LWGEmplace Return TypeOuluComplete4.0 p0088r3LWGVariant: a type-safe union for C++17OuluComplete4.0 + p0137r1CWGCore Issue 1776: Replacement of class objects containing reference membersOuluComplete6.0 p0163r0LWGshared_ptr::weak_typeOuluComplete3.9 p0174r2LWGDeprecating Vestigial Library Parts in C++17Oulu p0175r1LWGSynopses for the C libraryOulu